Aspects of Ecology. 245 
Vegetation, in order to study its regeneration. This method fur¬ 
nishes an important parallel to the study of the development of 
vegetation on new or naturally cleared soils, and the phases of 
migration and competition can be studied at will, and, if desired, 
under controlled conditions as well. 
The “ migration circle ” is designed to record the migration of a 
species by dissemination or other propagation from an individual 
plant or group of plants as a centre. The centre is permanently 
fixed by driving a labelled stake, and the position of each plant is 
recorded on a chart corresponding with the circle, by means of 
radial tapes and corresponding lines on the chart. The denuded 
circle bears the same relation to the ordinary circle that the 
denuded quadrat does to the ordinary quadrat. The “ denuded 
circle,” it may be remarked, is necessary in studying migration in a 
formation in which closely crowded annuals predominate. 
All the above methods are, in our opinion, of the greatest 
value in studying vegetation, and Dr. Clements is to be congratulated 
on working them out. It may be thought that they would naturally 
occur to anyone who had to face the problem of the minute 
structure and development of vegetation, but the fact remains that 
no one has hitherto worked them out, probably because no one but 
Dr. Clements has clearly and explicitly recognised the fact that 
vegetation has a specific structure and development which can be 
recorded and studied by exact methods. One of us has applied 
most of the methods in question to more than one type of formation 
since the publication of Dr. Clements’ book, with the result of 
acquiring the conviction that the very close attention to the details 
of vegetation demanded leads to the recognition of features which 
would otherwise escape notice. The procedure may be compared 
to that of drawing a tissue-section under the microscope, which 
forces the attention to points of detail, often of great importance. 
Dr. Clements’ treatment of cartography (i.e., the making of 
vegetation maps, a map being distinguished from a chayt, in that 
the former records formations or regions of vegetation, while the 
jatter records individual plants) is somewhat meagre, confessedly 
so, since as he says, “no attempt is made to describe the general 
cartographic methods used by other ecologists, notably Flahault.” 
Our author is anxious that “cartographic methods should be clear 
and simple, and that they should be uniform, so that charts and 
maps of widely separated formations may be directly compared 
without difficulty.” No doubt these are very desirable objects, but 
